The present invention relates to cameras.
In particular the present invention relates to a camera which preferably is of focal plane type and which can have connected thereto a strobe or electronic flash assembly.
When operating a photographic camera, particularly of the focal plane shutter type, with an electronic flash assembly, it is usually necessary to change over from the synchro contact to the X contact and to preset into the camera a shutter-time which is an appropriate time for electronic flash photography, such a time being referred to as the X time which is equal to a given fraction of a second. Such an X time is usually selected so as to be a relatively substantial exposure time equal to or greater than from 1/125 to 1/60 sec. As is well known, a focal plane shutter primarily provides a so-called slit exposure while the electronic flash provides a source of flash illumination the flash duration of which is extremely short so that only 1/2 to 1/4 of the photographed scene can be illuminated by the flash illumination in the event that the scene or object is photographed with a shutter speed or exposure time which is less than 1/250 sec. It is in order to eliminate this latter drawback that the X time is generally between 1/250 and 1/60 sec., as pointed out above.
However, with camera structures of the above type the operator often fails to preset the shutter so as to provide an exposure time which is suitable for electronic flash operation. A considerable inconvenience is often the fact that such a failure to preset the exposure time not discovered during operation of the camera but rather only after the film is developed.
A further drawback conventionally encountered with electronic flash photography resides in the fact that a variation of the distance from the camera to the object which is photographed results in a corresponding variation of the light reflected from the object, so that the diaphram of the camera must be reset in accordance with such a variation. In order to avoid this drawback, there are known electronic flash units which are automatically adjustable in accordance with reflected light received thereby, such units being known as so-called autostrobes which have recently been developed and in which a photometric circuit is associated with the flash tube so that when the latter provides flash illumination the light reflected from the object which is to be photographed is measured by the photometric circuit and operation of the electronic flash unit is automatically terminated when the measured light received from the object provides the proper exposure level.
Although electronic cameras generally include a photometric circuit, such a photometric circuit which is incorporated into the electronic camera is of no use when operating with flash illumination without utilizing an electronic flash which can automatically respond to the light reflected from the object which is photographed to terminate the flash when a sufficient amount of light has been provided thereby. The photometric circuit of the camera is not operative at such a time inasmuch as the camera is set for manually providing a predetermined exposure time suitable for flash illumination as pointed out above.
In the case where the photographic camera has an automatically controlled shutter and a photometric circuit which is combined with an automatic electronic flash of the above type, the X contact is closed with a predetermined time lag with respect to the starting of the running of the leading curtain of the shutter, and of course the electronic flash begins to provide flash illumination upon closing of the X-contact, the operation of the shutter being controlled by the electronic circuit which determines the sum of the natural available light and the artificial flash illumination. More specifically, upon depression of the shutter-tripping button of the camera, first the leading shutter curtain starts to run and, when the leading shutter curtain uncovers the film the X-contact is closed causing the electronic flash to provide flash illumination. When the available natural light and the flash illumination reflected from the object to be photographed obtain a proper level for exposure, the control magnet which prevents release of the trailing shutter curtain is deenergized so that the trailing curtain can now run down to terminate the exposure. In this way an exposure is completed.
In the event that the natural available light exceeds the amount of light required for proper exposure before closing of the X-contact a flash stopping signal is applied to the electronic flash unit. However, a certain inconvenience is encountered in the case where the natural available light reflected from the object to be photographed suddenly increases with the result that the electronic flash will still provide an undesirably excessive illumination by way of the flash illumination provided thereby upon closure of the X-contact, depending upon the timing relationship between generation of the flash stopping signal and closure of the X-contact. The result is that a film frame is partially covered by the trailing shutter curtain while the rest of the frame is overexposed, since the trailing shutter curtain has already entered into and extends across the path of film exposing light.